Mapping of stereoselective recognition sites on human serum transferrin by capillary electrophoresis and molecular modelling

Abstract

Stereoselective recognition of chiral compounds can be used for mapping of surface interaction sites on proteins. Iron-free human serum transferrin is a suitable chiral selector in capillary electrophoresis used in native form in solution. Separation of optical isomers of tryptophan-methylester, tryptophan-ethylester and tryptophan-butylester and various drugs were studied in capillary zone electrophoresis applying a distinct transferrin zone prior to sample injection. Changes in the electrophoretic patterns (i.e., in the migration properties) of the molecules reflected the possible interactions with the protein. The tryptophan derivatives and eight drugs possessed stereoselective interactions, seven drugs showed interactions without appreciable chiral separation, and the others did not present any direct complexation with the protein molecules. Molecular modelling was performed to characterize the binding areas at the iron binding site of iron-free transferrin. The docking of tryptophan derivatives on transferrin showed that the R-enantiomers possess a stronger complexation with transferrin, whereas the S-enantiomers are bound by weaker interactions, which is in excellent agreement with the capillary electrophoresis results, where the R-enantiomers were always retarded stronger by transferrin. A ranking of drugs by the lipo score parameter of the docking shows an accordance with the stereoselective interactions by the protein.

Identification and Quantitation of Enantiomers by Capillary Electrophoresis and Circular Dichroism Independent of Single Enantiomer Standard

“…Computational studies can be fruitfully applied to solve chirality related problems, especially when enantiomerically pure reference standards are missing . For example, quantitative structure–property relationship modeling was applied to predict enantiomer migration orders of amino acid esters and aromatic amino acids in CE. , However, this approach is limited to enantioseparation achieved with a chiral selector of which structure is available. One-dimensional dynamic computer simulation was employed to investigate the separation and migration order of ketoconazole enantiomers in CE, but this method is more suitable to describe 1:1 chemical equilibria between solutes and a buffer additive .…”

Chiral Separations

“…www.annualreviews.org • Chiral Separations (50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61). Racemization during storage, handling (62), or in vivo (63) is always a potential issue that makes it necessary to perform analytical testing of chiral compounds.…”

“…Perhaps the most valuable feature of the use of chiral additives is its straightforward ability to access chiral analyte-chiral selector binding information (56,137). Binding constants for the individual enantiomers in a racemic mixture with chiral additives can be determined by TLC (138), HPLC (139), and CE (137,140) within the same experimental protocols.…”

Recent advances in the study of biomolecular interactions by capillary electrophoresis

“…Many serum proteins such as BSA, HSA, serum albumin from other species, glycoproteins such as a-acid glycoprotein, crude ovomucoid, ovoglycoprotein, avidin, and riboflavin binding protein, enzymes such as fungal cellulose, cellobiohydrolase I, pepsin, and lysozyme and other proteins such as casein, human serum transferrin and ovotransferrin etc. can be used as chiral selectors in CE to separate drug enantiomers [105][106][107]. In the enantiomeric separation of ofloxacin, verapamil, and propranolol, using HSA or BSA as the buffer additive, the adsorption to the capillary wall by the protein was the key factor in the separation of ofloxacin enantiomers.…”